Systems for evacuating fluids having gaseous and vapor phases from large condensers of turbine-driven power plants, for instance, frequently use cooling liquid, such as water, from the same source as does the system being evacuated. In such systems, the temperature of the gas/vapor evacuated from the condenser may approach the temperature of the cooling liquid in the evacuating system. This may occur, for example, when the condenser operates at low load.
When the vapor and gases are compressed in a liquid ring pump in such an evacuating system, the heat of compression and condensation is transferred to the liquid in the pump which, within a closed system, is circulated from the pump through a cooler or heat exchanger back to the pump as seal liquid for the pump. The cooler in the system thus-far described has the capability of cooling the liquid in the evacuating system to below the temperature of the gas/vapor mixture as it enters the pump. However, if the cooling liquid for the heat exchanger of the evacuating system, drawn from the same source as the cooling liquid for the evacuated system, approaches too close to the temperature of the gas and vapor mixture from the evacuated system, saturation of the vapor with liquid from the seal will diminish the capacity of the pump.
A concomitant problem arises in the prior art attempt to cool the seal liquid of the pump using only a heat exchanger with cooling liquid. That problem is excessive cooling liquid consumption.